The present invention relates to a switching system, or more in particular, to a fixed-length packet switching system with the test function for maintenance suitable for the speech path module or the like of the broadband ISDN exchanger.
A switching system for handling fixed-length packets (hereinafter referred to as "the cells") generally comprises a switch including a plurality of input and output ports for distributing input cells among output ports according to the destination, a plurality of line interfaces for transferring the cells received from input lines to said input ports and the cells output from the switch output ports to output lines, and a controller for controlling the switch and the line interfaces.
In a method for testing the normality of the switching function of this type of switching system, for example, a test cell generated by the controller is input to one of the input ports of the switch. The switch transfers the test cell to a given line interface circuit, which is operated to loop back the test cell from the output line to the input line and input to the switch again. The switch is thus caused to transfer the test cell to the controller so that the controller checks whether the test cell has been received.
According to this method, the routing function for each output port of the switch and the function of each line interface circuit can be inspected by rewriting the routing information set in the header of the test cell.
Nevertheless, the problem of this method when applied to a switching system with a plurality of switch units connected in multiple stages is that in the case where the test cell cannot be received by the controller or the controller receives an abnormal cell, it is difficult to discover which switch unit of the multistage switch structure has a fault. There have been related art such as U.S. Pat. Nos. 5,124,977 and 5,184,346 both entitled "Switching System" in relation to ATM Switching System using common buffer memory.